Field of the Invention
The present invention relates to an intervertebral disk prosthesis. More particularly this invention relates to a three-part intervertebral disk prosthesis for the total replacement of an intervertebral disk of the cervical and lumbar spine.
Brief Description of the Related Art
An intervertebral disk prosthesis has at least a lower plate and an upper plate having anchor formations on their sides facing toward the adjacent vertebral bodies in case of a two-part prosthesis. A three-part-prosthesis comprises further an intermediate or middle plate. Neighboring plates articulate via their surfaces that get in contact. Thus, the parts of an intervertebral disk prosthesis are also designated as sliding partners, wherein the intermediate sliding partner arranged between upper and lower sliding partner represents an intermediate sliding plate.
The U.S. Patent Application Publication No. 2009/0082867 A1 of Bueno et al discloses a prosthesis with basically 3 articulating sliding partners, in which the intermediate sliding partner has no function for keeping the central distance between the upper and lower plate. Upper and lower sliding partner have both spherical convex inner surfaces, which are identical with the exception that the upper convexity has a hole housing a pivot of the lower sliding partner, wherein the pivot ends in a sphere. An intermediate partner having a central opening is arranged between the inner surfaces of upper and lower sliding partner. The surfaces of the intermediate partner facing the inner surfaces of upper and lower sliding partner are concave-shaped. The clearance between central opening of the intermediate partner and the pivot of the lower sliding partner may be dimensioned with one value for the anterior-posterior direction of the vertebral segment and another value for the lateral direction of the vertebral segment. A prosthesis according to US 2009/0082867 A1 has no means for limiting rotation around the vertical body axis and comprises only curved articulation surfaces. Further the pivot in the hole is directly limiting the range of extension and flexion as well as the range of lateral bending to both sides.